Increasing-decreasing Regulations And Control Reaearch Of Endogenous Formaldehyde Content In Lentinus Edodes

In recent years, formaldehyde in Lentinus edodes has caused widespread concern. Formaldehyde is a metabolite in Lentinus edodes; GGT and C-S lyase were the two key metabolic enzymes in the formation of formaldehyde. This research optimize and set up the detection of formaldehyde content in Lentinus edodes, study the growth and decline of endogenous formaldehyde in the Lentinus edodes growth stage and postharvest storage, and use UHP new production technology to regulate formaldehyde content in dried mushrooms; the major findings are as follows:The paper studied extraction method and standing time of mushroom homogenate, derivative time and derivative temperature in detection process, indicated the optimum conditions:Sample homogenate ultrasonic extraction for30min in an ice bath environment, an hour later centrifuge for10min at10000rpm in4℃, the derivative reaction time60min and the reaction temperature60℃.The methodology validation showed that the method is accurate and reliable. Contrast classical detection methods, the results showed the formaldehyde measured value of this HPLC detection is the lowest levels of all, the reason is that in heating, distillation, shaking and other pre-treatment process, the enzyme activities will increase, while HPLC experimental method can effectively inhibit the increase of enzyme activity during the test, simplify detection steps and improve the accuracy of inspection greatly. Using the improved method to investigate formaldehyde background levels of edible fungi, the result showed that formaldehyde content was not dectected in other samples of edible mushrooms expect Lentinus edodes, there were6.82-10.64mg-kg-1in fresh Lentinus edodes, the cotent were much higher in dry Lentinus edodes (184.55mg-Kg-1)The growth and decline of formaldehyde in Lentinus edodes were examined at growth phase and postharvest storage. The endogenous formaldehyde content increased significantly from mycelium period, basically achieved stable in half parachute stage. The endogenous formaldehyde content was6.51mg-Kg-1in parachute phase. Formaldehyde is the metabolite in Lentinus edodes, in post-harvest storage, endogenous formaldehyde levels increased because of metabolic activity, then decreased.The effect of different storage conditions was also studied. GGT and C-S lyase activity had a significant positive correlation with respiration rate (related coefficient:0.695and0.682respectively) and formaldehyde levels (related coefficient:0.667and0.675respectively).In Low-temperature storage, GGT and C-S lyase activities could be inhibited, and endogenous formaldehyde content could also be controlled. During16days of storage, formaldehyde levels of low-temperature and room temperature samples were11.26and6.63mg-Kg-1respectively. Meanwhile, low-temperature can effectively reduce respiration rate, decrease the loss of water and protein content, slow metabolism activity, stable acid-base balance of fruiting bodies environment, and improve the quality of Lentinus edodes. The result of different packing method showed that vacuum environment would increase respiration rate and the loss of protein content, raise fruiting bodies acidity during storage, what's more, increase formaldehyde levels.16days of storage, formaldehyde levels of vacuum and control samples were41.35and6.63mg-Kg-1respectively. The reason was that vacuum increased respiration rate, destroyed metabolic regulation in Lentinus edodes, which led to the increase of C-S lyase——which determined the formation of formaldehyde——enzyme activity. Besides, Vacuum environment is not conducive to the volatilization of formaldehyde.Use UHP technology to control formaldehyde content in dried m ushrooms. The result showed that at the end of hot air drying, the GGT and C-S lyase enzyme activities of UHP (400MPa,7.5min) preliminary treatment samples were4.17and26.08umol· g-1, which were44.52%and46.75%lower than control samples (P<0.01), the formaldehyde content was56.30mg·Kg-1, which was83.62%less than control samples (P<0.01). The GGT and C-S lyase enzyme activities increased sharply in the later period. The reason was that in the last1.5hours of hot air drying, samples temperature reached37℃around, which was the optimum temperature of GGT and C-S lyase. Generalize a conclusion:UHP preliminary treatment could destroy the non-covalent bond of protein structure, reduce the activities, significantly inhibited the increase of formaldehyde content(p<0.01).Sulfur-containing heterocyclic compounds, especially lenthionine (easy to decompose into dimethyl sulfide and dimethyl sulfide),1,2,4-trithiolane and1,2,4,5-tetrathiane were the most important flavor compounds in Lentinus edodes, which was also the production of GGT and C-S lyase zymohydrolysis. The relative amount of sulfur-containing heterocyclic compounds in control samples had an increase after hot air drying, There were considerable differences between control and UHP samples (in UHP samples, dimethyl sulfide and dimethyl trisulfide were not found;1,2,4-trithiolane and1,2,4,5-tetrathiane decreased26.41%and 97.62%).These results indicated that UHP preliminary treatment could significantly inhibit the GGT and C-S lyase enzyme activities, decrease formaldehyde and sulfur-containing compounds of Lentinus edodes during hot air drying process.